SS-CFU, SS-CFB, SS-CFNR and SS-CD are supplementary services which permit a served user to have the PISN send all or specific incoming calls addressed to the served user's PISN number to another number.

Service specifications are produced in three stages and according to the method specified in ETS 300 387. This Standard contains the stage 3 specification for the Q reference point and satisfies the requirements identified by the stage 1 and stage 2 specifications in ECMA-173.

The signalling protocol for SS-DIV operates on top of the signalling protocol for basic circuit switched call control, as specified in ECMA-143 and uses certain aspects of the generic procedures for the control of supplementary services specified in ECMA-165.

This Standard also specifies additional signalling protocol requirements for the support of interactions at the Q reference point between SS-DIV and other supplementary services and ANFs.

This Standard is applicable to PINXs which can be interconnected to form a PISN.

The protocol defined in this Standard forms part of the PSS1 protocol (informally known as QSIG).